| 1. |
- Andersson, Magnus, et al.
(författare)
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Fiskbestånd och miljö i hav och sötvatten : Resurs- och miljööversikt 2012
- 2012
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Detta är den nionde utgåvan av den samlade översikten över fisk- och kräftdjursbeståndens status i våra vatten. Kunskap om fiskbestånden och miljön är en förutsättning för att utnyttjandet av fiskresurserna skall bli bärkraftigt. För svenska vattenområden beskrivs miljöutvecklingen i ett ekosystemsperspektiv, dels för att tydliggöra fiskens ekologiska roll och beskriva yttre miljöfaktorer som påverkar fiskbestånden, dels för att belysa fiskets effekter på miljön.Fiskbestånd och miljö i hav och sötvatten är utarbetad av Sveriges lantbruksuniversitet (SLU), Institutionen för akvatiska resurser (SLU Aqua), på uppdrag av Havs- och vattenmyndigheten. Rapporten sammanfattar utveckling och beståndsstatus för de kommersiellt viktigaste fisk- och kräftdjursarterna i våra vatten. Bedömningar och förvaltningsråd är baserade på Internationella Havsforskningsrådets (ICES) rådgivning, SLU Aquas nationella och regionala provfiskedata, samt yrkesfiskets rapportering.
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| 2. |
- Bryhn, Andreas, et al.
(författare)
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A continuous involvement of stakeholders promotes the ecosystem approach to fisheries in the 8-fjords area on the Swedish west coast
- 2017
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Ingår i: ICES Journal of Marine Science. - : Oxford University Press (OUP). - 1054-3139 .- 1095-9289. ; 74, s. 431–442-
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Tidskriftsartikel (refereegranskat)abstract
- The coastal marine environment in the 8-fjords area on the Swedish west coast has been subjected to various stakeholder co-management initiatives since 1999. Stakeholders and authorities have acted by supporting and implementing gradually stricter fishing restrictions following the collapse in the 1970s of several demersal fish stocks and their apparent lack of recovery. Moreover, concerns have been raised regarding a locally sharp depletion of eelgrass meadows, in addition to an apparent increase in the number of seals and cormorants. The present 8-fjords initiative applies a cross-sector approach to environmental management and thus also addresses various types of environmental pollution. This study has compared the environmental work around the 8-fjords to 15 principles regarding the ecosystem approach to fisheries (EAF). The main strength that has been identified among the EAF principles is the continuous involvement of stakeholders. Among weaknesses in the EAF is the scarcity of suitable indicators that are necessary for appropriate monitoring, especially biomasses of functional groups as well as economic and social indicators. Many environmental problems in the fjords remain and it is possible that improved adherence to EAF principles will facilitate solving some problems and alleviating others. Moreover, the application of the EAF in practice in the 8-fjords can serve as a guiding example for co-managing other aquatic ecosystems towards ecological, economic, and social sustainability. The experiences from the 8-fjords initiative, including its extensive stakeholder involvement, may serve as a practical EAF example to be studied by researchers and managers globally.
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| 3. |
- Östman, Örjan, et al.
(författare)
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Förvaltningsmål för nationellt förvaltade fiskbestånd : En översikt av kvantitativa mål
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Fisk - och skaldjursbestånd som i huvudsak är begränsad e till svenska nationella vat- ten förvaltas av svenska myndigheter och organisationer. Dessa bestånd kan i motsats till internationellt exploaterade och förvaltade arter utnyttjas av flera olika aktörer (t.ex. kommersiellt - och fritidsfiske) . Olika grupper av aktö rer kan ha olika syn på vad som är de lämpligaste långsiktiga förvaltningsmålen (t.ex. stor avkastning vs. stora individer). För dessa nationella bestånd är ofta datatillgången sämre än för in- ternationella bestånd, och ofta saknas tydliga mätbara förvaltni ngsmål, vilket resul- terar i en mindre effektiv förvaltning. Syftet med denna rapport är att ge en överblick över tillgängliga kvantitativa förvaltningsmål med tillhörande metoder som är lämp- liga för ett långsiktigt hållbart utnyttjande av nationella fisk - och skaldjursbestånd. Vi identifierar tre huvudkategorier av kvantitativa förvaltningsmål: 1) Långsiktigt hållbar avkastning, som kräver detaljerade data från många olika källor . 2) Minini- våer av biomassa - eller abundansindex, eller ett specifikt förhållan de mellan fångst och biomassaindex, vilket kräver pålitlig övervaknings - eller fångstdata. 3) "Natur- lik" eller "önskvärd" demografisk struktur, vilket kräver information om egenskaper så som storlek, ålder, och könsmognad. Alla tre typer na av mål har sina förtjänster och nackdelar. Mål för hållbar avkastning och biomassa -index tar inte hänsyn till storleksstruktur, och vice versa, och olika mål kräver olika typer av indata. Vi gör en översikt av vilka förvaltningsmål som kan vara lämpliga för olika typer av nationellt förvaltade fisk - och skaldjursbestånd. För närvarande är aktuell a data i allmänhet allt- för begränsade för att föreslå specifika förvaltningsmål för de flesta bestånd som kan komma i fråga för nationell förvaltning. Snarare betonar vi vikten av att använda flera olika mål i stället för att förlita sig på ett enda för att underlätta en hållbar användning av akvatiska resurser med hänsyn tagen till olika intressenter. Dessutom finns det ingen klar definition av vad ett nationellt bestånd är och när det är lämpligt att ha en nationell förvaltning. Därför är det viktigt att förvaltningsmålen sätts så att de kan återspegla både internationella, nationella och lokal a förutsättningar .
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| 4. |
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| 5. |
- Andersson, Magnus, et al.
(författare)
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Movements, recapture rate and length increment of tagged pikeperch (Sander lucioperca) - a basis for management in large lakes
- 2015
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Ingår i: Fisheries Management and Ecology. - : Wiley. - 0969-997X .- 1365-2400. ; 22, s. 450-457
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Tidskriftsartikel (refereegranskat)abstract
- Movements, site fidelity, exploitation rate and total length (TL) increment of pikeperch, Sander lucioperca L., were studied by tagging 3977 pikeperch, of 334mm mean TL, in Lake Malaren in 1994. Fish were recaptured in gillnets, trap nets and to a lesser extent with rod and line. Total recapture rate was 30.4%, with 50% of the recaptures made within 8.4km of the release site. Movements were restricted during summer, whereas movements from shallow to deeper basins were frequent in autumn. The yearly TL increment was estimated at 99mm for fish 300mm long at release and 42mm for fish of 400mm at release. The results have direct implications for future management, as the mortality of undersized fish in the fishery; the strong site fidelity and fast growth indicate that fishery closures may be an effective measure to attain a larger stock of fish above the size limit.
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| 6. |
- Bergek, Sara, et al.
(författare)
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Fiskfångster och utsättningar av fisk
- 2012
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Ingår i: Vänern: årsskrift 2012. ; :73, s. 68-73
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Totalfångsten i yrkesfisket i Vänern ökade under 2011 med drygt 8 procent jämfört med 2010. Den viktigaste arten för yrkesfisket gösen, stod för cirka 32 procent av totala fångstens värde. Fångsten av siklöja och signalkräfta ökade medan fångsten av abborre, gädda, gös, öring, sik och ål minskade. De registrerade fritidsfiskarna fångade under 2011 totalt 70 ton, en minskning med 14 ton jämfört med 2010. Något fler lax- och öringsmolt sattes ut jämfört med föregående år. Även utsättningen av ål ökade, hela 605 000 stycken försträckta alternativt karantäniserade ålyngel sattes ut under 2011.
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| 7. |
- Bergström, Ulf, et al.
(författare)
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Long-term decline in northern pike (Esox lucius L.) populations in the Baltic Sea revealed by recreational angling data
- 2022
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Ingår i: Fisheries Research. - : Elsevier BV. - 0165-7836 .- 1872-6763. ; 251
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Tidskriftsartikel (refereegranskat)abstract
- In the Baltic Sea, the large predatory fish northern pike (Esox lucius L.) is important for both recreational fisheries and ecosystem functioning. As existing fishery-independent surveys do not adequately monitor pike populations, a general lack of knowledge on population status and trends poses challenges for management. Here we use recreational angling data as an alternative method to describe pike population development along the Swedish Baltic Sea coast from 1938 onwards and assess the change over time in potential mortality factors by estimating harvest by fisheries and consumption by large predators. Data from a Swedish national register on trophy-sized pike (>12 kg) showed that numbers and maximum sizes peaked in 1990-1995, after which declines in both metrics are evident. In logbooks from a sport fishing club in the Stockholm archipelago, a simultaneous decrease in maximum sizes of pike was observed, together with a decrease in the total number of pike caught per fishing day. Jointly, these data indicate a decline in the abundance of large pike since around 1990. While commercial pike fisheries in the Baltic Sea have decreased continuously since the 1950s, recreational fishing increased after 1985, when Swedish coastal waters were made open access to anglers. The declines in large pike starting in the 1990s could, thus, have been driven by an increase in mortality from recreational fisheries, which at the time primarily practiced catch and kill. Since the 2000s, bag and slot length limits, spawning closures, and a general increase in catch-and-release fishing has reduced the landings of pike in recreational fisheries. Despite these fisheries regulations and higher release rates the decline in catches of large pike has continued, indicating an effect of other mortality factors. The strong growth of grey seal (Halichoerus grypus) and great cormorant (Phalacrocorax carbo sinensis) populations suggest that predation pressure on pike has increased over time. In the Stockholm archipelago these two predators were estimated to remove 5-18 times (range based on different diet composition estimates) more pike biomass than total fisheries landings in 2014-2017. To improve the situation for northern pike in the Baltic Sea managers need to consider both fisheries restrictions and measures to decrease predation pressure and increase recruitment. Catch data from recreational fisheries may be used to evaluate such management efforts by providing information on the population development of this keystone species.
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| 8. |
- Bryhn, Andreas, et al.
(författare)
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Modelling the biomass of functional groups of fish in an archipelago bay of the Baltic Sea
- 2013
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Ingår i: Ecological Modelling. - : Elsevier BV. - 0304-3800 .- 1872-7026. ; 269, s. 86-97
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Tidskriftsartikel (refereegranskat)abstract
- Fish biomass estimates in European coastal waters are necessary for several reasons, e.g., for meeting requirements in legislation and international agreements, for establishing sustainable outtakes of the resources, for developing management plans and for assessing the ecological and environmental status of coastal waters. This study estimated piscivorous and non-piscivorous fish biomass as well as total fish biomass in Kvadofjarden Bay on the Swedish Baltic Sea coast using dynamic foodweb modelling. Weight-per-unit-effort data from the coastal fish monitoring program in the area together with a range of abiotic variables (including salinity and total phosphorus) were used as drivers for the CoastWeb model. To further refine the estimates of fish biomass, we complemented the model by using data from nearby areas on the ratio of piscivorous to non-piscivorous fish for those size classes not representatively sampled by the monitoring gear (fish < 12 cm). Piscivorous fish biomass in the area was estimated at 10-14 tonnes (4.6-6.5 kg/ha), non-piscivorous fish biomass at 105-139 tonnes (47-62 kg/ha) and the subsequent total fish biomass was estimated at 115-154 tonnes (52-69 kg/ha). The estimated range of total fish biomass was comparable with findings from other investigations on the Swedish Baltic Sea coast which used a coarser methodology. The method presented in this paper can be used for making biomass estimates in other coastal waters where passive gears are used to monitor the local fish communities, and could thus serve a range of purposes for assessing the production and status of fish in coastal waters. (C) 2013 Elsevier B.V. All rights reserved.
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| 9. |
- Faulks, Leanne, et al.
(författare)
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Intraspecific Niche Variation Drives Abundance-Occupancy Relationships in Freshwater Fish Communities
- 2015
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 186:2, s. 272-283
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Tidskriftsartikel (refereegranskat)abstract
- A positive relationship between occupancy and average local abundance of species is found in a variety of taxa, yet the mechanisms driving this association between abundance and occupancy are still enigmatic. Here we show that freshwater fishes exhibit a positive abundance-occupancy relationship across 125 Swedish lakes. For a subset of 9 species from 11 lakes, we estimated species-specific diet breadth from stable isotopes, within-lake habitat breadth from catch data for littoral and pelagic nets, adaptive potential from genetic diversity, abiotic niche position, and dispersal capacity. Average local abundance was mainly positively associated with both within-lake habitat and diet breadth, that is, species with larger intraspecific variation in niche space had higher abundances. No measure was a good predictor of occupancy, indicating that occupancy may be more directly related to abundance or abiotic conditions than to niche breadth per se. This study suggests a link between intraspecific niche variation and a positive abundance-occupancy relationship and implies that management of freshwater fish communities, whether to conserve threatened or control invasive species, should initially be aimed at niche processes.
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| 10. |
- Holmgren, Kerstin, et al.
(författare)
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Impacts of climate warming on the long-term dynamics of key fish species in 24 lakes
- 2012
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Ingår i: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 694, s. 1-39
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Forskningsöversikt (refereegranskat)abstract
- Fish play a key role in the trophic dynamics of lakes. With climate warming, complex changes in fish assemblage structure may be expected owing to direct effects of temperature and indirect effects operating through eutrophication, water level changes, stratification and salinisation. We reviewed published and new long-term (10-100 years) fish data series from 24 European lakes (area: 0.04-5,648 km(2); mean depth: 1-177 m; a north-south gradient from Sweden to Spain). Along with an annual temperature increase of about 0.15-0.3A degrees C per decade profound changes have occurred in either fish assemblage composition, body size and/or age structure during recent decades and a shift towards higher dominance of eurythermal species. These shifts have occurred despite a reduction in nutrient loading in many of the lakes that should have benefited the larger-sized individuals and the fish species typically inhabiting cold-water, low-nutrient lakes. The cold-stenothermic Arctic charr has been particularly affected and its abundance has decreased in the majority of the lakes where its presence was recorded. The harvest of cool-stenothermal brown trout has decreased substantially in two southern lakes. Vendace, whitefish and smelt show a different response depending on lake depth and latitude. Perch has apparently been stimulated in the north, with stronger year classes in warm years, but its abundance has declined in the southern Lake Maggiore, Italy. Where introduced, roach seems to take advantage of the higher temperature after years of low population densities. Eurythermal species such as common bream, pike-perch and/or shad are apparently on the increase in several of the lakes. The response of fish to the warming has been surprisingly strong and fast in recent decades, making them ideal sentinels for detecting and documenting climate-induced modifications of freshwater ecosystems.
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